Steam generators of pressurized-water nuclear reactors comprise a bundle of U-shaped bent tubes whose straight legs must be maintained in parallel arrangements along the whole height of the bundle.
Each of the straight legs of each of the tubes of the bundle is fitted into a set of aligned openings of a set of tube support plates arranged in positions at a distance from one another along the height of the bundle. The openings passing through the tube support plates form regular arrays, for example with square or triangular meshes.
The passage openings must be shaped so that they simultaneously allow a tube to be supported effectively and for the steam generator feed water to flow around the tube, through the tube support plate.
The openings passing through the tube support plates may be of complex shapes, for example a trefoil shape.
The bundles of a high-power steam generator comprise a large number of tubes, for example of the order of 5,000, so that each of the tube support plates has a very large number of passage openings separated by metal sections which may be of relatively small thickness.
The passage openings in the tube plates must therefore be produced by a process which at the same time makes it possible to obtain very accurately shaped and sized openings, which is fast, and which can be easily carried out automatically.
The openings in the tube support plates are generally produced by broaching, i.e., by passing a profiled broach which has a cross-section corresponding to the section of the opening through each of the rough-drilled holes of an array of cylindrical rough-drilled holes passing through the plate.
The broaches which are moved in their axial direction through the rough-drilled holes comprise cutting ridges which make it possible to carry out the machining of the openings, generally as a single cut.
There are known broaching plants which comprise a support for holding and positioning the plate in a broaching position and means for moving the plate on its support in at least two directions parallel to the faces of the plate in working position, so as to place each of the rough-drilled holes successively on the axis of a broach secured to one of its ends in a traction device and at its other end in an accompanying device, the traction device and the accompanying device being situated on either side of the plate to be broached.
The traction device and the accompanying device comprise means for guiding and moving in a common axial direction perpendicular to the plate.
After each of the broaching operations performed by moving the traction and accompanying devices, the end of the broach must be separated from the accompanying device before the broach is completely released from the plate by a complementary movement of the traction device. The plate is moved away from the zone in which the traction device and the accompanying device move. The broach can then be refitted and secured in the accompanying device before being replaced in an initial broaching position.
The plate is then replaced in a new broaching position, generally by employing means for moving in at least two directions parallel to the faces of the plate.
To increase the performance speed of the broaching plant a number of broaches can be secured simultaneously to a unit consisting of a traction device and an accompanying device for carrying out the broaching of a number of openings simultaneously.
However, the production capacity of the broaching plants is limited by the fact that between two broaching operations it is necessary to separate the broach from the accompanying device, to take the broach out of the plate, to move the plate away, to replace the traction device and the accompanying device in their initial position and to move the plate towards a new broaching position.
This means that the effective plate broaching operations are separated by relatively long time intervals at the expense of production capacity and of plant efficiency.
In particular, the movement of the traction and accompanying devices to restore them to an initial position requires a time which is of the same order as the time needed to carry out the broaching.
To increase the production capacity of the broaching plants it has been proposed, in FR-A-2,407,780, to employ two parallel broaching lines, each comprising a traction device and an accompanying device which simultaneously perform the broaching of two openings or of two sets of openings in the plate.
The traction and accompanying devices of the two lines are placed in inverse arrangements on either side of the plate, so that the two lines function in opposite directions, the broaching being performed simultaneously, on two sets of openings, from either side of the plate. At the end of a broaching operation the two broaches or the two sets of broaches are turned around and transferred from a traction device to an adjacent accompanying device.
A relatively complex handling device must therefore be employed for turning the broaches around and transferring them.